480 AN AMERICAN TEXT-HOOK OF PHYSIOLOGY. 



air on entering and leaving the calorimeter; while the estimate of the heat lost 

 in evaporating water involves the measurement of samples of the air entering 

 and leaving the instrument and of the quantities of water in both eases, the 

 total quantity of water evaporated from the animal being estimated from these 

 data. 



The conduct of such experiments is not attended with any material dif- 

 ficulties. The water of the calorimeter is stirred for a suffieient length of 

 time in order to obtain a uniform temperature. The temperature of the 

 animal is taken and the animal then placed within the animal chamber. The 

 temperatures of the calorimeter and of the air entering and leaving the instru- 

 ment, and readings of the three gas-meters are recorded. During the progress 

 of the experiment air temperatures are recorded at regular intervals of ten or 

 fifteen minutes and the water stirred for a few seconds each time. At the 

 conclusion of the experiment there are recorded — the temperature of the calori- 

 meter, the temperatures of the air entering and leaving the calorimeter, the 

 quantities of air passing through the three gas-meters, and the temperature of 

 the animal. 



The quantity of heat given to the calorimeter \> now determined by multi- 

 plying the increase of temperature of the instrument by the calorimetric 

 equivalent. If the rise of temperature be 0.6° C. and the calorimetric equiva- 

 lent be 90 kilogramdegrees, the quantity of heat imparted to the water jacket 

 will be 90 X 0.6° = 54 kilogramdegrees. 



The quantity of heat imparted to the air is determined by finding first the 

 corrected volume of the air, then reducing the corrected volume to weight, 

 then multiplying the weight by the specific heat of air at 0° C, and finally 

 multiplying by the increase of temperature. The corrected volume may be 



V P 



obtained by the following formula: V= — , where V is 



760 (1 + 0.003665 t) 

 the required volume at 0° C. and 760 mm. barometric pressure, V the ob- 

 served volume, P the observed pressure, and t the observed mean temperature: 

 760 (1 + 0.00366-0 is conveniently obtained from standard tables. The errors 

 incident to changes in barometric pressure and in aqueous tension are so slight 

 that they are not usually taken into consideration. Assuming that the quan- 

 tity of air supplied amounted to 6000 liters, and that the mean temperature 

 of the air was 20°, the corrected volume would be, omitting barometric 



V 6000 



pre— nre and aqueous tension, V = — — = 5590 liters 



(1 + 0.0036656 t) 1,0733 

 at 0° C. One liter of dry air at 0° C. weighs 0.001293 kilogram ; therefore, 

 559* I liters x 0.001293 = 7.22s kilograms. 1 1' we assume that the air during 

 its passage through the calorimeter had its temperature increased 3°, and the 

 specific heat of air is O.L > :',77. the quantity of heat imparted to the air must 

 have been 7.228 x 3 x 0.2377 = 5.152 kilogramdegrees. 



The next estimate is of the quantity of heat lost in the evaporation of 

 water. This is determined by finding the difference between the quantities 



